1. Field of the Invention
The present invention relates to an electric hammer drill that can switch operation modes to perform predetermined processing works on a work-piece.
2. Description of the Related Art
A known electric hammer drill to switch between a hammer mode and a hammer-drill mode is disclosed in Japanese non-examined laid-open Patent Publication No. 2002-192481. In the known electric hammer drill, a piston is caused to reciprocate within a cylinder via a crank mechanism driven by a motor. Then, a striker is linearly driven via air spring and the striking movement is transmitted to the tool bit via an intermediate element. Further, a rotation transmitting mechanism is provided which transmits rotation of the motor from an intermediate shaft to the tool bit via the cylinder and a tool holder. A clutch mechanism is disposed in the rotation transmitting mechanism and is adapted to transmit rotation of the motor to the tool bit by engaging clutch claws and to prevent such transmission of rotation to the tool bit by disengaging the clutch claws. Further, a mode changing mechanism is provided which serves to switch the clutch mechanism between the state of transmitting rotation and the state of preventing the transmission of rotation. When the mode changing mechanism is switched to the hammer mode, the rotation of the tool bit is prevented so that an operation solely by a striking movement of the tool bit can be performed. When the mode changing mechanism is switched to the hammer-drill mode, rotation is transmitted to the tool bit so that an operation by a combined movement of striking and rotating can be performed.
Generally, in an electric hammer drill in which the cylinder and the motor are arranged within the tool body such that the respective axes run generally crossing to each other to form “L” shape, the center of gravity of the electric hammer drill is positioned below the axis of the cylinder and slightly forward of the axis of the motor. The user performs a predetermined operation by holding a handgrip on the opposite side of the tool bit, and a side handle. The greater the distance between the center of gravity and the axis of the cylinder, the larger the vibration in the longitudinal direction (the longitudinal direction of the cylinder) or in the vertical direction. In the known electric hammer, the intermediate shaft of the rotation transmitting mechanism that transmits rotation of the motor to the cylinder (the tool bit) is placed forward of the motor and below the cylinder. The clutch mechanism that serves to releasably transmit the rotation is placed on the intermediate shaft. Further, the mode changing mechanism that serves to switch the clutch mechanism between the engaged state and the disengaged state is placed near the clutch mechanism. Thus, the components for switching the operation modes of the tool bit are centralized in one area. In such a case, the weight of the lower part below the axis of the cylinder is further increased and the balance of weight is tipped. Thus, the center of gravity of the electric hammer drill is displaced farther downward away from the axis of the cylinder. Therefore, the known electric hammer is in difficulty to decrease operating vibration.